Abstract
In recent years, mountain rack railways have emerged in China, showcasing their remarkable climbing capabilities with maximum gradients reaching 250‰ to 480‰, over ten times that of conventional railway trains. The core components of rack railway trains are the rack bogies and rack drive systems, whose performance and reliability are critical to the success of the trains’ development and operational safety. To thoroughly validate the functionality, quality, and safety of these components, pre-installation bench tests are essential. However, China previously lacked a specialized test platform for such studies. This paper, by analyzing the characteristics and functional requirements of the rack drive system, presents the research and design of a rack drive system test platform. It introduces the platform’s main functions, principles, and structure, describing its overall architecture, mechanical, hydraulic, electrical, testing, control, and monitoring systems. The key features, technological innovations, and application scenarios of the test platform are also summarized. The successful establishment and application of this test platform fills a gap in China’s rack drive test capabilities, enhancing the experimental means for rack vehicle drive systems and marking a significant step forward in the development of rack drive systems.
1. Introduction
Advancing a multi-level, multi-modal rail transit network is a vital strategy to promote national new-type urbanization and foster the integrated development of urban agglomerations and metropolitan areas. In recent years, a new mode of rail transit—mountain rack railways—has emerged in China, with several local governments expediting their planning and construction.
Mountain rack railways, as their name implies, are specifically designed for steep terrain, with maximum gradients reaching 250‰ to 480‰, far exceeding the capabilities of conventional railway trains. Rack railway trains, therefore, require strong climbing abilities, with their defining feature being the rack bogies. The core of these bogies lies in the rack drive system, whose performance and reliability are paramount to the success of rack railway train development.
The rack drive system is a highly complex component, with no mature domestic products available, necessitating brand-new design and development. Consequently, pre-installation bench tests are crucial to validate its functionality, quality, and safety. However, China lacked a dedicated test platform for rack drive systems. This paper addresses this gap by presenting the research and design of a rack drive system test platform, aimed at conducting performance and reliability studies.
2. Structure and Characteristics of the Rack Drive System
The rack drive system builds upon the technology platform of current mainstream urban rail vehicle wheelset drive systems, adopting a similar motor suspension + gearbox bracing structure. It incorporates additional components such as rack wheels and rack braking devices to interact with the rack rail, providing greater traction and braking forces during steep gradients. The system primarily consists of wheelsets, axle boxes, transmission gearboxes, clutch mechanisms, drive gears, bracing mechanisms, band brakes, traction motors, and coupling devices。
3. Overall Architecture of the Rack Drive System Test Platform
3.1 Functional Requirements
The primary functions of the test platform are to simulate the rack drive system’s operation under different rack and wheel-rail conditions, subject to varying traction or braking loads, and apply specific vibration and shock excitations as per standard requirements. It can conduct various types of tests, including rack function tests, traction and braking characteristic tests, temperature rise tests, transmission efficiency tests, overspeed and overload tests, durability vibration and shock tests, rack-to-wheel-rail switching tests, and simulated steep gradient traction and braking capability tests.
3.2 General Design
The rack drive system test platform is a single-wheelset roll-vibration test bench with rack drive functionality. It utilizes a track wheel to simulate an infinite-length steel rail and a large circular rack gear to mimic the intermediate infinite-length rack of the actual line. The test subject is vertically compressed onto the track wheel through a simulated framework, with longitudinal flexible positioning achieved by front and rear traction positioning devices. Bi-directional driving simulates the movement of the wheelset and rack wheel on the track. The test platform comprises mechanical, hydraulic loading, electrical, testing and monitoring。
3.3 Traction Positioning Devices
The traction positioning devices, one set at the front and another at the rear, serve to provide longitudinal positioning for the test subject drive system. These devices consist of reaction frames, traction rods, embedded platforms, and guiding rails. The traction rods can be adjusted vertically along the T-slots installed on the reaction frame plates, allowing for adaptability to different heights of the test subjects. The tension can be regulated by adjusting the length of the screws, ensuring stable and secure positioning during testing.
3.4 Simulated Loading Devices
The simulated loading devices are designed to apply vertical loads to mimic the actual axle weight of the test subjects. They consist of a loading gantry and a simulated framework. The gantry is constructed to withstand loads up to 21 tons, ensuring structural integrity during heavy-duty tests. The simulated framework is designed with a modular structure, allowing for easy replacement of components based on different test requirements. This versatility ensures that various drive systems can be tested efficiently with minimal setup time.
4. Hydraulic Loading System
The hydraulic loading system is composed of a hydraulic power unit, vertical loading cylinders, a control system, and piping valves. This system applies vertical downward loads to the simulated framework, simulating the actual axle weight of the test subject. The dual cylinders allow for independent or synchronized control, providing flexibility in testing scenarios. Key parameters of the hydraulic loading system include:
- Rated Pressure: 21 MPa
- Maximum Vertical Load: 2 × 150 kN
- Cylinder Speed: 0 – 200 mm/min
- Cooling Method: Air Cooling
5. Electrical System
The electrical system of the test bench can be divided into seven subsystems: power supply, transmission, auxiliary, testing, control, hydraulic electrical and control unit, and video surveillance. The main components include low-voltage switchgear, rectifier transformers, frequency converters, three-phase step-up transformers, drive motors, measurement cabinets, control consoles, air compressors, fans, torque sensors, temperature sensors, and acceleration sensors. The electrical system architecture is depicted in Figure 10, showcasing the integration of various components into a cohesive system.
6. Testing System
The testing system is responsible for collecting critical parameters during the test, such as vibrations, temperatures, and stresses of the flywheel box, gearbox, and track wheel bearings. It comprises a paperless recorder, temperature scanners, dry-type transformer temperature controllers, voltage and current sensors, temperature sensors, acceleration sensors, IEPE signal conditioners, an industrial computer with communication and acquisition cards, and other related equipment. The testing system architecture is illustrated , showcasing the comprehensive nature of the data acquisition and monitoring capabilities.
7. Control System
The control system is the central nervous system of the test bench, overseeing the logical control and protection of the entire system. It consists of an industrial computer in the control console, a main PLC S7-1215, a hydraulic loading PLC S7-1200, and S7-200Smart PLCs in the measurement cabinets. The industrial computer processes and displays test data, issues operational commands, and manages the overall control flow. The main PLC handles logic control, frequency converter regulation, and system protection. The S7-200Smart PLCs execute commands from the main PLC and collect status information from various cabinets. The control system architecture and network layout are detailed.
8. Video Surveillance System
The video surveillance system monitors critical loading points, wheel-rail movement, and the test area, providing real-time visual feedback to the control room. This system ensures that operators can promptly respond to unexpected events and document any incidents for future analysis. A total of five video capture points are installed, and the display interface is shown 。
The authors successfully designed and implemented a rack drive system test platform to cater to the emerging demand for mountain rack railways in China. The test platform is essential for validating the functionality, reliability, and safety of the rack drive system, which is the core component of rack trains. These trains are capable of navigating steep gradients of up to 250‰ to 480‰, surpassing the capabilities of conventional railway trains by over tenfold.
The test platform simulates various operational conditions of the rack drive system, including different track gauges, axle loads, and speed levels. It performs tests such as rack function tests, traction and braking characteristic tests, temperature rise tests, transmission efficiency tests, overspeed and overload tests, durability vibration and shock tests, and simulated high-gradient traction and braking capability tests.
The platform’s architecture comprises mechanical, hydraulic, electrical, testing, control, and monitoring systems. The mechanical system features adjustable track wheels and rack gears, allowing for simulations of diverse rail conditions. The hydraulic loading system simulates the actual axle weight, while the electrical system controls and measures various parameters during testing. The control system integrates PLCs for logical control and protection, ensuring seamless operation.
Innovations include the adaptability of the test platform to both wheel-rail and rack-rail conditions, its ability to simulate steep gradients, and the modular design of its mechanical components for easy maintenance and reconfiguration. Additionally, the platform incorporates energy-saving features, such as regenerative braking, which can recover and reuse braking energy, resulting in over 70% energy savings during testing.
The successful establishment and application of this test platform not only fills the domestic void in rack drive testing but also elevates the country’s experimental capabilities in this field. It enables rapid iterative development of core technologies for rack trains and significantly contributes to enhancing the safety and reliability of these vehicles.
In conclusion, the research and design of this rack drive system test platform represent a significant advancement in the development of mountain rack railways in China, paving the way for further innovations and advancements in the railway industry.